Traffic signal lights are extensively used in the United States, and throughout the world, to control the flow of traffic on roadways. Although traffic signal lights are relatively simple and commonplace, they are critical for ensuring the safety of the driving public. Traffic signal lights improve highway safety and reduce congestion by providing for the orderly and predictable movement of traffic through intersections.
There are over six million individual traffic lights controlling traffic throughout the United States. It is important to ensure a proper operation, and adherence of these lights to standardized specifications The light intensity, directivity, and other specifications for traffic signal lights used in the United States have been established in standards from the Institute of Transportation Engineers (ITE). Many traffic signal lights, currently in operation, fail to meet their expected performance levels. Such failed signals frequently are not mere variations from the ITE standards specifications; but frequently are major departures from those standards.
Traffic signal lights fail to meet ITE specifications for a number of different reasons. For example, if the lamp voltage is low, the condition generally results in reduced candle power at all measurement angles. Deterioration of the reflector by distortion seriously reduces the candle power or intensity of the light emanating from the lens. Traffic signal reflectors generally are parabolic in form, and use lamps placed at or close to the parabolic focal point to produce rays in a generally parallel direction striking the lens. The lens design relies on these parallel rays to produce the final required light distribution from the signal light. If the reflector becomes distorted or diffuse, the light rays no longer are parallel, and there is a widening of the final light pattern. This causes considerable loss of candle power values near the center of distribution from the lamp.
Another reason for failure is in deterioration of the lens. When the signal lens deteriorates because of vapor etching, burning or general wear and tear, there is likely to be a reduction in the center range of the candle power values caused by diffusion of some or all of the light rays in the beam.
If the lamp is not properly located on the optical axis of the reflector by either shifting it in or out, the rays leaving the reflector, again, deviate from their normally parallel pattern. This type of shifting also affects the center high candle power values significantly. If the lamp is improperly inserted, so that it shifted to one or the other sides of the optical axis of the reflector, the filament is misaligned with the axis. This causes a sideways shifting, or a skew in the final light rays, either to the right or to the left. The result is a reduction in the candle power values emanating from the lens.
A final error resulting in failure to meet ITE specifications is improper lamp installation. For example, if a 67 Watt lamp, intended for an 8" traffic signal light, is placed into a 12" traffic signal light, rated for 150 Watt lamps, a significant degradation in performance on the low side results from the signal light. Similarly, if a 150 Watt rated lamp is placed in an 8" traffic signal light fixture, designed for a 67 Watt lamp, an excessively high value of light emanating from the fixture will initially result. This, however, can result in burning or darkening of the lens, and possible warping or deterioration of the reflector, resulting in permanent degradation of the traffic signal light.
Additional reasons exist for the failure of a traffic signal light to perform up to standards. Some of these reasons are dirt accumulation on the optical parts, such as the reflector and the lens; incorrect rotational orientation of the lens, which changes the angular direction of the light emanating from the lens; or deterioration of the optical parts, such as warping or other damage to the reflector and the like.
Typically, testing traffic signal lights for conformity with the ITE specifications cannot be done on any reasonable basis in the field, that is, at the operating location of the traffic signal light. Laboratory equipment is well known for laboratory testing traffic signal light assemblies for conformity with ITE specifications; but such equipment is bulky and requires precise alignment to the traffic signal lens for accurate and effective testing. To do this on location, at a street intersection, requires a lane closure, a platform truck, regulated power supplies, and perfect stabilization of the suspension mounted traffic signal lights. Consequently, testing of traffic signal lights after installation rarely is done.
It is desirable to provide a simple and effective device for testing installed traffic signal lights to determine the performance levels of such lights by means of a portable, easy-to-use device.